We focus on the NLU component, and we generalize several recent approaches assuming that the output of the NLU process is a partially filled semantic frame [1]}, [2]}, corresponding to the intent of the user in a certain portion of the dialogue, with a number of slot-value pairs that need to be filled to accomplish the intent.
The notion of intent originates from the idea that utterances can be assigned to a small set of dialogue acts [3]}, and it is now largely adopted to identify a task or action that the system can execute in a certain domain. Slot-value pairs, on the other end, represent the domain of the dialogue, and have been actually implemented either as an ontology [4]}, possibly with reasoning services (e.g. checking the constraints over slot values) or simply trough a list of entity types that the system needs to identify during the dialogue.
